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Irrigation Principles
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Gravity
Terms in this set (25)
The law of conservation of mass can be applied to obtain the water balance of the soil root zone
True
Nitrate nitrogen in irrigation water should be credited toward fertilizer requirements of plants
True
Water movement from the soil, through the plant, and into the atmosphere is primarily caused by differences in water potential
True
Latent heat flux is hear absorbed by liquid water to change into a gaseous state.
True
The Maximum depth of plant-available water is the difference between plant depth of water at saturation and depth of water at permanent wilt point
False
Irrigation should be applied when the soil water deficit (D) is greater than the depth of management allowed depletion (d MAD)
True
At a given matric potential, the equilibrium soil water content is less when the soil is drying than when the soil is wetting
False
If the rate of rainfall or irrigation is greater than the infiltration rate of the soil, then water will be lost through surface runoff
True
The apparent specific gravity of soil is numerically equal to saturated hydraulic conductivity
False
Water flow measurement is based on the conservation of velocity between two sections of the flow path
False
_____is the flow of mass, volume, or energy per unit time that can be calculated by multiplying an exchange conductance by the gradient.
Flux
Which soil property can be used to convert moisture content dry mass basis (theta g) to moisture content by volume (Theta v)?
Soil bulk density
Which element can cause soil particles to disperse and lead to reduced water infiltration?
Sodium
Which component of total soil water potential will always have a zero value when the soil is unsaturated?
Hydrostatic pressure potential
The root zone of turf grass has a previous days deficit of 0.83 inch. For the current day, turf grass ET is 0.22 inch while precipitation is 0.35 inch. There is no irrigation. What is the current soil water deficit?
0.70
0.83+0.22=1.05 -0.35=0.70
The maximum depth of plant available water is soil water that exists between ____ and permanent wilting point
Field Capacity
Irrigation is applied using a sprinkler system. The sprinklers run at a constant application rate for 20 minutes per irrigation cycle. At what time (t) after the start of irrigation would you expect the least possibility of getting runoff?
t= 1 minute
According to the law of conservation of mass (continuity equation), when water flows from a small diameter pipe into a larger-diameter pipe, the velocity of flow will________
Decrease
A ____________ is a device that measures the matric potential of soil
tensiometer
The water characteristic function gives the relationship between matric potential and ______
Soil water content
The lower limit of plant-available soil moisture; normally approximated at a matric potential of -15 bars.
permanent wilting point
Water is flowing in a rectangular canal that is 1.5 feet wide. Using portable propeller meter, you estitmate the average flow velocity to be 1 ft/s. What other information would you need to estimate the volume flow rate?
Depth of water canal
It was determined that a loam soil had a current moisture content of 0.16, dry mass basis (theta g). The bulk density of the soil is 1.40 g/cm^3 and the root zone depth is 60cm. It was determined from lab analysis that the moisture content by volume is 0.31 at field capacity and 0.14 at permanent wilting point. Determine the following;
a. Current soil moisture content by volume (Theta v)
b.current depth of water in the root zone (dw, cm)
c. If MAD= 0.4, what is the depth of water that is allowed to be depleted (dMAD,cm)
d. Soil water deficit (D, cm)
e. Is irrigation required? If so, how much water (cm) should be applied for the root zone to reach field capacity?
a. (theta v) = (Theta g ) * (Pb / Pw)
0.16*(1.40/1) = 0.224
b. dw= (theta v) * depth of root zone
0.224*60=13.44 cm
c. 0.4*10.2 = 4.08cm
d. dpwp= .14*60 = 8.4
d FC = .31*60= 18.6
D=dfc-dw
18.6-13.44 = 5.16cm
e. Yes, irrigate because D is greater than dMAD add 5.16 cm
Beans are being grown using irrigation water having an electrical conductivity (ECw) of 1.5 dS/m. Beans can tolerate soil - extractable water with an electrical conductivity (ECe) of 1.0 dS/m without any yield reduction. Determine the following;
a. Leaching requirement (LR, decimal fraction) to flush excess salths from the root zone
b. Applied water or gross irrigation requirement (inches) needed to flush salts if the current soil water deficit (D) is 0.9 inch
a. LR= ECw/(5
ECe-ECw) = 1.5dS/m / (5
1.0-1.5) = 0.4286
b. AW= D/1-LR = 0.9/ (1-0.4286) = 1.575 inches
Water is flowing full in a circular pipe that is supplies a sprinkler system. The pipe has an inside diameter (d) of 0.083 ft. The velocity of flow is 7.0 ft/s. Determine the following;
a. Volume flow rate ( q, ft^3/s)
b. If the sprinkler system runs at the above flow rate for 20 minutes, what total volume of water applied (ft^3)
a. A= pi
d^2/4 =pi
(0.83)^2 /4 = 0.0054
q= VA
= 7*0.0054
=0.0378 ft^3/s
b. = 0.0387*1200s=45.36ft^3
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